1. Field of the Invention
The present invention relates to an apparatus for crack splitting an annular part, such as the big-end of a connecting rod, by use of a fixed expander jaw and a movable expander jaw for engaging the bore formed by the annular part, and by use of an expander device urging the expander jaws apart.
2. Description of the Related Art
An apparatus for crack splitting an annular part is known, for example, from European patent document nos. EP-0 396 797 and EP-0 661 125. Such devices serve to split an integral annular part, in this case the big-end of a connecting rod, by cracking it into two parts, i.e., into a cap and rod. These known devices include expander jaws whose peripheral surface area is in full contact with the inner surface area of the big-end bore. Such a full contact of the expander jaws with the bore is generally deemed necessary for a neat split.
The peripheral surface area of the expander jaws of the present invention is configured such that the expander jaws engage the inner surface area of the bore only via a precisely localized partial surface area or linear portion, so that the cracking response can be influenced.
Tests have indicated, surprisingly, that best crack splitting is not always achievable by full contact of the peripheral surface area of the expander jaws with the inner surface area of the bore. Instead, it may be advantageous, depending on the material of the annular part and its cracking response as well as other parameters, such as the geometry of the fracture surface area, to introduce the cracking force only into a specific partial surface area portion or line of the piece concerned. Thus, it may be expedient to introduce the cracking force to only partial or linear surface areas, either axially or circumferentially into the bore. In special instances it may also be advantageous to introduce the cracking force both axially and circumferentially.
Tests have also surprisingly indicated that such a configuration prevents double fractures, crumbling and snags from materializing when nuisance geometry involving bores, holes and the like exists within the crack surface, as is often experienced with known devices. For instance, big-ends feature two holes in the region of the crack surface for bolting the cap and rod together after splitting. When splitting is initiated, the crack flows from the crack initiating crevice, which is provided in the region of the inner surface area of the bore in manufacturing the connecting rod, laterally around the bolting holes outwards. The crack surfaces reunite behind the bolting holes. However, since the crack surfaces fail to be automatically propagated in the same plane on both sides of the bolting holes, double cracks, crumbling and snags may materialize when the crack surfaces reunite. Such double cracks, crumbling and snags are to be avoided.
The partial surface area or line portion via which the cracking force is introduced can be configured in many different ways. Defining or optimizing the particular configuration and localization may be done by trial and error. Thus, for instance, the partial surface area of the expander jawsxe2x80x94as viewed in the radial direction of the borexe2x80x94may be barreled or conical. The radius of the expander jaws may also be larger than the radius of the bore in the annular part to compensate for the so-called contraction effects.
For particular applications it may be expedient to provide an elastic material at the peripheral surface area of the expander jaws. This elastic material may extend partially or entirely over the peripheral surface area. Tests have indicated that, depending on the particular application, the elastic material may have a hardness of 50 to 95 Shore A. For special applications, it may be advantageous to configure the elastic material in the form of a sleeve. This sleeve may be arranged, for example, centered relative to, or concentric with the inner surface area of the bore. Due to this arrangement of the elastic material, peak stresses resulting in uncontrolled crack propagation can be prevented. Providing elastic material may also be particularly suitable in cases where the bore of the annular part needs to be split in the non-machined condition. For specific applications, the elastic material may also be arranged in the form of elastic segments on the peripheral surface area of the expander jaws.
The expander device may also be configured such that each expander jaw has two-parts, i.e., an expander jaw core and an expander jaw shell. The outer surface area of the expander jaw shell engages the inner surface area of the bore in the annular part. In such a configuration, the outer surface area of the expander jaw shell may or may not be cylindrical.
The advantage of configuring the expander jaws with a core and shell is that the apparatus can be adapted very simply to annular parts of differing shape and size. This merely requires the expander jaw shell to be changed, whereas no change to the expander jaw core, including the expander device, is required. It is also possible to influence the cracking response simply by swapping the expander jaw shell. Thus, to achieve a specific crack where necessary for an identical annular part, the expander jaw shell can be swapped with another having a differently shaped outer surface area. This can be repeated until the desired, optimum cracking response is attained.
Expander jaw shells can be produced in many different ways. One particularly simple and cheap embodiment is achieved by machining the expander jaw shell as a turned component which is split into two or more ring segments in a subsequent operation.
In principle, the expander jaw shell or its ring segments are securable to the expander jaw core in many different ways. For example, each expander jaw shell can be flanged at one edge for receiving the retaining devices, such as fastener bolts, quick-release fasteners, or the like.
As described above, the present invention makes it possible to introduce the cracking force into the annular part such that initiation and propagation of the crack are defined, thus enabling the cracking response to be precisely influenced. In this respect, by varying the geometry of the expander jaws in accordance with the present invention, the cracking response can be influenced both in any non-machined and in any rough-machined or finished condition of the bores and holes in the annular part.